A center display that serves as a display unit for a navigation device and an audio device is a typical example of display units mounted on vehicles. Other examples include a meter-type display unit for displaying a vehicle speed, a rotation speed of an engine, or the like. Further, in recent years, a vehicle having a head-up display in which information is displayed on a windshield has been studied (refer to, for example, Patent Literature 1).
The inventor of the present application has found the following knowledge regarding the information display system. On the display units described above, different pieces of information are respectively displayed. Examples of the pieces of information displayed on these display units include important information related to safety of a person on the vehicle, information used for driving the vehicle, information for obtaining convenience and comfort, and information for satisfying interests and preference of the person on the vehicle. Therefore, in a configuration in which different pieces of information are displayed respectively on a plurality of display units, it is required to prioritize important information whose relation to safety is stronger, and cause a driver to perceive such important information. However, in a configuration in which there are multiple display units, a driver does not necessarily see a display unit on which important information to be perceived is displayed. In particular, when different pieces of information are displayed on the multiple display units at the same time, the driver may possibly miss a display unit on which important information to be perceived is displayed.